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Web caches can be used in various systems (as viewed from direction of delivery of web content):

Forward position system (recipient or client side)

A forward cache is a cache outside the webserver's network, e.g. on the client software's ISP or company network.[2]

A network-aware forward cache is just like a forward cache but only caches heavily accessed items.[3]

A client, such as a web browser, can store web content for reuse. For example, if the back button is pressed, the local cached version of a page may be displayed instead of a new request being sent to the web server.

A web proxy sitting between the client and the server can evaluate HTTP headers and choose to store web content.

Google's cache link in its search results provides a way of retrieving information from websites that have recently gone down and a way of retrieving data more quickly than by clicking the direct link.

allows a response to be used without re-checking it on the origin server, and can be controlled by both the server and the client. For example, the Expires response header gives a date when the document becomes stale, and the Cache-Control: max-age directive tells the cache how many seconds the response is fresh for.

Validation

can be used to check whether a cached response is still good after it becomes stale. For example, if the response has a Last-Modified header, a cache can make a conditional request using the If-Modified-Since header to see if it has changed. The ETag (entity tag) mechanism also allows for both strong and weak validation.

Invalidation

is usually a side effect of another request that passes through the cache. For example, if a URL associated with a cached response subsequently gets a POST, PUT or DELETE request, the cached response will be invalidated.

Many CDNs and manufacturers of network equipment have replaced this standard HTTP cache control with dynamic caching.